From: Uros Bizjak <ubizjak@gmail.com>
Date: Thu, 9 Oct 2025 18:44:17 +0000 (+0200)
Subject: x86_64: Use __seg_fs qualifiers in PTR_{MANGLE,DEMANGLE}() macros
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=60e3ada68d316828adcf50f81ef290ed15f1512d;p=thirdparty%2Fglibc.git

x86_64: Use __seg_fs qualifiers in PTR_{MANGLE,DEMANGLE}() macros

Use __seg_fs named address space qualifiers in PTR_MANGLE() and
PTR_DEMANGLE() macros to access the pointer_guard field in the TCB.

This change allows the compiler to eliminate redundant reads of
the variable, reducing the number of reads from 98 to 89 and
decreasing the text size of the library by 512 bytes.

While at it, fix a few trivial whitespace issues as well.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---

diff --git a/sysdeps/unix/sysv/linux/x86_64/pointer_guard.h b/sysdeps/unix/sysv/linux/x86_64/pointer_guard.h
index 9cf79a4703..485066d64d 100644
--- a/sysdeps/unix/sysv/linux/x86_64/pointer_guard.h
+++ b/sysdeps/unix/sysv/linux/x86_64/pointer_guard.h
@@ -26,35 +26,46 @@
 /* We cannot use the thread descriptor because in ld.so we use setjmp
    earlier than the descriptor is initialized.  */
 # ifdef __ASSEMBLER__
-#  define PTR_MANGLE(reg)       xor __pointer_chk_guard_local(%rip), reg;    \
-                                rol $2*LP_SIZE+1, reg
-#  define PTR_DEMANGLE(reg)     ror $2*LP_SIZE+1, reg;                       \
-                                xor __pointer_chk_guard_local(%rip), reg
+#  define PTR_MANGLE(reg)	xor __pointer_chk_guard_local(%rip), reg;     \
+				rol $2*LP_SIZE+1, reg
+#  define PTR_DEMANGLE(reg)	ror $2*LP_SIZE+1, reg;			      \
+				xor __pointer_chk_guard_local(%rip), reg
 # else
-#  define PTR_MANGLE(reg)       asm ("xor __pointer_chk_guard_local(%%rip), %0\n" \
-                                     "rol $2*" LP_SIZE "+1, %0"                   \
-                                     : "=r" (reg) : "0" (reg))
-#  define PTR_DEMANGLE(reg)     asm ("ror $2*" LP_SIZE "+1, %0\n"                 \
-                                     "xor __pointer_chk_guard_local(%%rip), %0"   \
-                                     : "=r" (reg) : "0" (reg))
+#  include <stdint.h>
+extern uintptr_t __pointer_chk_guard_local attribute_relro attribute_hidden;
+#  define PTR_MANGLE(var) do						      \
+    {									      \
+      (var) = (__typeof (var)) ((uintptr_t) (var)			      \
+				^ __pointer_chk_guard_local);		      \
+      asm ("rol $2*" LP_SIZE "+1, %0" : "+r" (var));			      \
+    } while (0)
+#  define PTR_DEMANGLE(var) do						      \
+    {									      \
+      asm ("ror $2*" LP_SIZE "+1, %0" : "+r" (var));			      \
+      (var) = (__typeof (var)) ((uintptr_t) (var)			      \
+				^ __pointer_chk_guard_local);		      \
+    } while (0)
 # endif
 #else
 # ifdef __ASSEMBLER__
-#  define PTR_MANGLE(reg)       xor %fs:POINTER_GUARD, reg;                   \
-                                rol $2*LP_SIZE+1, reg
-#  define PTR_DEMANGLE(reg)     ror $2*LP_SIZE+1, reg;                        \
-                                xor %fs:POINTER_GUARD, reg
+#  define PTR_MANGLE(reg)	xor %fs:POINTER_GUARD, reg;		      \
+				rol $2*LP_SIZE+1, reg
+#  define PTR_DEMANGLE(reg)	ror $2*LP_SIZE+1, reg;			      \
+				xor %fs:POINTER_GUARD, reg
 # else
-#  define PTR_MANGLE(var)       asm ("xor %%fs:%c2, %0\n"                     \
-                                     "rol $2*" LP_SIZE "+1, %0"               \
-                                     : "=r" (var)                             \
-                                     : "0" (var),                             \
-                                       "i" (POINTER_GUARD))
-#  define PTR_DEMANGLE(var)     asm ("ror $2*" LP_SIZE "+1, %0\n"             \
-                                     "xor %%fs:%c2, %0"                       \
-                                     : "=r" (var)                             \
-                                     : "0" (var),                             \
-                                       "i" (POINTER_GUARD))
+#  include <tls.h>
+#  define PTR_MANGLE(var) do						      \
+    {									      \
+      (var) = (__typeof (var)) ((uintptr_t) (var)			      \
+				^ ((tcbhead_t __seg_fs *)0)->pointer_guard);  \
+      asm ("rol $2*" LP_SIZE "+1, %0" : "+r" (var));			      \
+    } while (0)
+#  define PTR_DEMANGLE(var) do						      \
+    {									      \
+      asm ("ror $2*" LP_SIZE "+1, %0" : "+r" (var));			      \
+      (var) = (__typeof (var)) ((uintptr_t) (var)			      \
+				^ ((tcbhead_t __seg_fs *)0)->pointer_guard);  \
+    } while (0)
 # endif
 #endif